Depth of field viewing, as described in U.S. Pat. No. 5,400,177, is accomplished by enhancing depth cues which are present in every flat image, whether photographed or recorded electronically, without the requirement of special glasses, eye shutters or similar devices used in front of the viewers eyes. The depth cues are enhanced by a specially designed prismatic screen that separates the viewer's eye focus and convergence. The separation triggers the brain of the viewer to disregard convergence information indicating that the screen is flat, and to interpret the image depth cues as real.
To strengthen the focus and convergence separation and add additional image magnification, the preferred embodiment of the present invention utilizes a specially designed magnifying lens as a supplement to the prismatic screen. The lens helps trigger the eye focus and convergence separation--making it stronger when combined with a prismatic screen such as is disclosed in U.S. patent application Ser. No. 08/155,748, filed Nov. 23, 1993, now U.S. Pat. No. 5,400,177. In addition, depending upon the particular design of the lens, the viewed image may magnified from 1.25.times. to 2..times., and at the same time is cleared (cleaned) from the magnified raster of the video scanning lines. The clearing (cleaning) of the viewed image from the magnified raster is accomplished with the prismatic screen, as described in the parent application. With particular reference to FIGS. 29 to 36 of that application, the prismatic screen PR preferably includes three miniature prisms for each video scan line. As a result, each raster video scan line is divided two or three times, thereby providing a significant reduction in the visibility of the raster lines. In accordance with the present invention, as described in greater detail below, the prismatic screen may be either a flat or curved structure, depending upon the choice of additional optical elements in the system.
A number of designs on how to magnify a video small screen image to a larger screen image are described in patent literature. For example U.S. Pat. No. 2,449,886 and U.S. Pat. No. 5,061,052 disclose such systems. Each of these designs are based on using a positive lens, or a lens combined with a Fresnel lens, and each technique places the optical system near the front of the video monitor screen. The lenses are designed with a short focal length which may cause distortion, because the magnification of the image is not equal in the center and on the edges. Additionally, the Fresnel lens, which is a concentric design of a magnifying lens, may cause image degradation by lowering the image resolution. According to U.S. Pat. No. 5,061,052, the described system is intended to allow individuals of limited means to enjoy the entertainment and education provided by large screen television images, without the necessity of purchasing a large television set. However, such prior art television magnification of a small screen image to a larger screen image may cause distortion and a poor image, particularly since these systems magnify the raster of scanned video lines which make up the image. When the lines are magnified, the image is degraded and becomes distorted, and eyestrain may result. These and other disadvantages of the prior art are overcome by the present invention.